In recent years, a chip antenna for Bluetooth® or GPS is incorporated in a small mobile terminal such as a mobile phone. The chip antenna of such a type is required to be small in size and easily be adjusted in terms of a resonance frequency thereof and advantageous in terms of impedance matching. This is because the resonance frequency and an input impedance of the chip antenna vary due to influences of a structure of a printed circuit board, various electronic components mounted around the chip antenna, and a casing, and thus, it is necessary to adjust the resonance frequency and input impedance for each model.
As a method of adjusting the resonance frequency and input impedance, there is known a method described in, e.g., Patent Document 1, in which a chip component such as a chip capacitor or a chip inductor is used. Further, Patent Documents 2 and 3 propose a frequency variable circuit using a varicap diode as a method of adjusting the resonance frequency.